1. Field of the Invention
The present invention relates to a system and a method of information communication, an information processing apparatus and an information processing method, a program and a recording medium, and more particularly to a system and a method of information communication, an information processing apparatus and an information processing method, a program and a recording medium, all for enabling the realization of surer NAT traversal.
2. Description of Related Art
Internet Protocol (hereinafter referred to as IP) is currently used as a routing protocol in the Internet. The most popular version of the IP is “4” (hereinafter referred to as IPv4) at present. The number of bits of a transmission source address and a transmission destination address which are used in this version is “32”. In an global network, typically the Internet, a transmission source address and a transmission destination address of communication data of communication performed between communication terminal apparatus are severally made to be absolutely identifiable by assigning an address of 32 bits based on the IPv4 (hereinafter referred to as an IPv4 address) uniquely to each communication terminal.
However, because of a rapid enlargement of the utilization coefficient of the Internet, there is the possibility of the run-out of the IPv4 addresses. Accordingly, for solving the problem, the Internet Engineering Task Force (IETF) laid down a protocol as the version 6 of the IP (hereinafter referred to as IPv6) and has started to spread the IPv6. However, it actually needs much time and cost for shifting routing protocols to be used in the Internet totally to the IPv6, and it is difficult to solve this problem completely.
Accordingly, as a technique for enlarging a range of available addresses while using the existing IPv4, a method using an address space having a local (private) property, that is, “private address” has been proposed.
That is to say, the private address is an address assigned to each terminal in a network within a predetermined limited range, that is, a private network, differently from the address assigned to each terminal apparatus in a global network uniquely or in a manner of “one and only”, (hereinafter referred to as a global address) as the IPv4 address. Each communication terminal, which is connected to the private network, and which a private address is assigned to, commonly owns a global address assigned to the private network.
Consequently, in a case where a communication terminal apparatus in a private network communicates with another communication terminal apparatus having a global address in the Internet by means of a private address, a process for converting the private address to a global address is needed. As a method for realizing the conversion, a network address translation (NAT) has been devised. In this case, each communication terminal is connected to a global network through the NAT.
Moreover, a method adopting a network address port translation (NAPT) has been also devised. The NAPT uses a port being a sub address (auxiliary address) provided below an address to convert a private address assigned to a communication terminal in a private network and a port (or a socket) to be used for communication to a global address and a port, respectively.
However, in a case of executing an application by which users need to communicate with each other directly, such as a video chat and an online game, (the so-called peer to peer (P2P) application) by using user terminals connected to private addresses in a private network, the so-called NAT traversal, in which the user terminals themselves obtain global addresses and ports, both converted by means of the NAT (or the NAPT), to perform communication, is needed.
A technique called as UPnP™ has been devised for solving a problem of this NAT traversal. UPnP™ is a function based on a protocol standardized by a UPnP™ forum. A communication terminal which is connected to a private network subordinate to the NAT and is mounted with the function can obtain a global address and a port, both converted by means of the NAT by performing communication defined by UPnP™.
Moreover, as another method for solving the problem of the NAT traversal, a technique called as Simple Traversal of UDP through NATs (STUN) has been also devised. According to STUN, a communication terminal connected to a local area network subordinate to the NAT obtains a global address converted by means of the NAT on the basis of the information obtained from a server (STUN server) connected to a global network.
Moreover, a technique for providing P2P communication by using a relay server and a router together with the NAT in a case where a terminal managed under a global address and a terminal managed under a private address perform communication with each other has been also proposed (see, for example, Patent Document 1).
[Patent Document 1] Japanese Patent Application Publication (KOKAI) No. 2001-345841.